The present invention generally relates to plasma guns, particularly to ablative plasma guns.
Electric power circuits and switchgear have conductors separated by insulation. Air space often serves as part or all of this insulation in some areas. If the conductors are too close to each other or voltage exceeds the insulation properties, an arc can occur between conductors. Air or any insulation (gas or solid dielectrics) between conductors can become ionized, making the insulation conductive thereby enabling arcing. Arc temperature can reach as high as 20,000° C., vaporizing conductors and adjacent materials, and releasing an explosive energy that destroys circuits.
Arc flash is the result of a rapid energy release due to an arcing fault between phase-phase, phase-neutral, or phase-ground. An arc flash can produce high heat, intense light, pressure waves, and sound/shock waves similar to that of an explosion. However, the arc fault current is usually much less in magnitude as compared to short circuit current, and hence delayed or no tripping of circuit breakers is expected unless the breakers are selected to handle an arc fault condition. Typically, arc flash mitigation techniques use standard fuses and circuit breakers. However, such techniques have slow response times and are not fast enough to mitigate an arc flash.
One other technique to mitigate arc fault is to employ a shorting (mechanical crowbar) switch, placed between the power bus and ground, or between phases. The crowbar switch shorts the line voltage on the power bus and diverts the energy away from the arc flash thus protecting equipment damage due to arc blasts. The resulting short on the power bus causes an upstream circuit breaker to clear the bolted fault. Such switches, which are large and costly, are located on the main power bus that shuts down the entire power system when a fault occurs even if the fault is only on the load side of a branch circuit. As a result, the mechanical crowbars are known to cause extreme stress on upstream transformers due to bolted fault condition.
There is a need for improved arc flash prevention mechanism that has an improved response time and that is cost effective.